1. Field of the Invention
The present invention relates to an automatic door system, and more particularly to an apparatus for controlling such a system.
2. Description of the Prior Art
A typical automatic door system has a door coupled with and driven by a belt extending from a drive pulley to its driven pulley. The drive pulley is driven by a reversible motor. Controlled rotation of the reversible motor provides automatic opening and closing of the door.
A prior art apparatus for controlling such a door system employs several switches mounted in the path of travel of the door at different position thereof. An activating member typically in the form of a dog is mounted on the door and successively turns the switches on or off when the door is advanced. One of the switches is adapted to indicate, when activated by the dog, to the system when to decelerate the motion of the door. Another one of the switches placed at the end of stroke of the door serves to stop the door. However, this arrangement requires accurate positioning of the switches as well as a laborious work of electrical connection thereto.
A door control system recently proposed by the Applicant (Japanese Patent Application No. 133383/81, filed Aug. 27, 1981) aims to eliminate such disadvantages and utilizes a tacho generator driven by the motor for driving the door. Pulses indicative of the speed of the motor and therefore the door are derived from the AC output waveform of the tacho generator. A counter counts up or down the pulses relative to a predetermined stroke of the door so as to produce the current position of the door. The control system provides a controlled deceleration and stop of the door in accordance with the detected current position of the door.
In general, an automatic door is decelerated to a low speed before it reaches either of its stroke ends so that the door will have a smoothed stop action at the stroke end to prevent hazard.
For this purpose, it has been practiced to determine an optimal bracking torque and an optimal deceleration point on the basis of the door weight and the mechanical sliding resistance of the door. The prior art control system employs a decelerating switch physically positioned at the determined deceleration point. The output signal of the switch is used to switch the system from a high speed mode of operation to a reduced speed mode.
In the system recently proposed by the Applicant, a deceleration point is internally set in an electrical component. When the current door position signal from the counter coincides with the set value of decelerated point, a reduced speed drive system is switched into operation.
However, the sliding resistance of a door not only depends on temperatures and wind pressure against the door but also varies with time due to such as deterioration of a guide rail for the door. This leads to variations in optimal braking torque and deceleration point. Therefore, in order to maintain an optimal performance of the door either of the above systems would require a troublesome manual adjustment either by changing the set value of the deceleration point by means of such as a variable electrical register or by repositioning the decelerating switch mounted in the path of door each time the sliding resistance of the door changes. In actuality, repetitive adjustments of deceleration point following the change of sliding resistance are too much trouble for an operator to do. Thus, an optimal performance of the door through an extended time of period cannot be obtained.